JP2007290000A - Flat die for form rolling of worm shaft - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flat die for the form rolling of a worm shaft in which a flat part of a predetermined width for a straightening die needs not be provided on a work adjacent to a circumferential surface form rolling part of a columnar material, and applicable works are not limited, while the bend of the work by the form rolling is small, and a step for straightening is unnecessary. <P>SOLUTION: The lead angle of a thread at a starting end of biting parts 30 of flat dies 6, 7 is set to be β1; the lead angle of a thread at a terminating end of finishing parts 31 of the flat dies is set to be β2, and the relationship of β1 < β2 is set. Threads are formed by continuously and smoothly changing the lead angle from the lead angle β1 of the thread at the starting end of the biting parts of the flat dies to the lead angle β2 of the thread at the terminating end of the finishing parts of the flash dies. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a flat die for rolling a worm shaft, which is a shaft with a worm gear.

2. Description of the Related Art Conventionally, a worm shaft, which is a shaft with a worm gear used for a small motor or the like, has a worm gear formed on a peripheral rolling portion of a cylindrical material by rolling. That is, the columnar material is moved in opposite directions while being pressed by a pair of dies, thereby rotating the columnar material and forming a worm gear on the peripheral surface rolling portion.
JP 2003-145242 A

  When the worm shaft is formed by the conventional rolling process, as shown in FIG. 1, which is a side view of an example of the worm shaft that has been subjected to the rolling process due to the weighted imbalance at the end of the rolling die, A bend 5 is generated at the twelve cut-off portions, that is, at the end portions of the peripheral surface rolling portion 2 of the cylindrical material. Since the bend 5 generated in the worm shaft 12 causes abnormal vibration and noise when incorporated in a small motor, a process such as bend removal correction is required to keep the bend 5 of the worm shaft 12 below a certain level. There were issues such as. As a method for solving such a problem, in Patent Document 1, in a flat die, each pair of straightening dies is brought into contact with a cylindrical portion adjacent to a peripheral surface rolling portion of a columnar material on both side surfaces of the flat die being rolled. A method of correcting the bending is proposed. However, in this method, it is necessary to provide a flat portion with a constant width as a pressing portion that presses the correction die adjacent to the worm shaft processing portion, that is, the peripheral surface rolling portion of the cylindrical material, The applicable work was limited. Further, in the worm rolling process, as the process progresses, there is a problem that the rolling diameter corresponding to the lead angle of the flat die is shifted, and the effective tooth width of the worm gear is shortened.

The problem of the present invention is that it is not necessary to provide a flat portion with a constant width for a straightening die adjacent to the peripheral surface rolling portion of the cylindrical material, which solves the conventional problem, and the applicable work is limited. An object of the present invention is to provide a flat die for a worm shaft rolling process that is not deformed and has a small workpiece bending due to a rolling process and does not require a process such as a bending correction.
Another object of the present invention is to provide a flat die for worm shaft rolling which can secure a necessary effective tooth width without shortening the effective tooth width of the worm gear due to a step by rolling.

  Therefore, the present invention provides a worm shaft rolling flat die that is arranged between a pair of flat dies and forms a worm gear on a peripheral rolling portion of a cylindrical material, and a thread at the leading end of the biting portion of the flat die. The lead angle of the flat die is set to β1, the lead angle of the screw thread at the end of the finished portion of the flat die is set to β2, and β1 <β2 is set. By providing a flat die for worm shaft rolling processing, wherein the thread angle is formed by continuously and smoothly changing the lead angle until the lead angle β2 of the thread at the end of the finished part is reached. The problem of the present invention described above has been solved.

  In the rolling process of worm shafts that do not use straightening dies, the circle in which the workpiece rolls without slipping during the rolling process is called a rolling circle. The diameter of this rolling circle, the rolling diameter D, is an experiment of rolling process. Is required. Further, when the lead angle of a flat die for processing a workpiece is β and the axial pitch of the worm gear is P, the relationship of tan β = P / πD is established. From the biting part to the finishing part, the material of the cylindrical material rises up to the tip of the worm gear, and the rolling diameter of the cylindrical material gradually increases. For this reason, when the lead angle β of the flat die is constant, there is a step in which the worm shaft moves in the axial direction due to the difference between the design rolling diameter D and the actual rolling diameter. The rolling diameter of the cylindrical material of the part <the rolling diameter of the finishing part, and the lead angle β1 of the chamfered part starting edge of the flat die <the lead angle β2 of the threading end of the finished part, and the flat die Since the lead angle is continuously and smoothly changed from the lead angle β1 of the chamfered portion start thread to the lead angle β2 of the finished end of the flat die, the thread is formed. It is possible to reduce the step in the fabrication process, and it is not necessary to provide a flat part with a constant width for the straightening die adjacent to the peripheral surface rolling part of the cylindrical material, and the applicable work is limited. Without In addition, the present invention provides a flat die for a worm shaft rolling process in which the bending of the workpiece due to the rolling process is small and a process such as bending correction is not necessary.

Preferably, in a flat dies for worm shaft rolling processing which is disposed between a pair of flat dies and forms a worm gear on the peripheral surface rolling portion of the cylindrical material, the outer diameter of the cylindrical material is D0, When the diameter is D3 and the root diameter of the worm gear is D4, the lead angle of the thread at the start of the bite portion of the flat die is β1, the design rolling diameter of the cylindrical material at the bite portion is D1, the axial direction of the worm gear Let P be the pitch.
The design rolling diameter of the cylindrical material at the biting part is D1,
(D0 × 0.95) <D1 <(D0 × 1.05) and β1 is set so that tanβ1 = P / πD1.
The lead angle of the screw thread at the end of the finished part of the flat die is β2, the designed rolling diameter of the cylindrical material at the finished part is D2, and the designed rolling diameter of the cylindrical material at the finished part is D2.
[(D3 + D4) / 2] <D2 <1.1 × [(D3 + D4) / 2]
And β2 is set so that tanβ2 = P / πD2.
In addition, the lead angle is continuously and smoothly changed from the lead angle β1 of the screw thread at the leading end of the flat die to the screw lead angle β2 at the end of the finish part of the flat die. As a result, the rolling diameter of the cylindrical material at the bite portion of the flat die approximates the diameter of the cylindrical material, and the rolling diameter of the cylindrical material at the finished portion is the outer diameter of the worm gear as D3. Since the root diameter of the worm gear is slightly larger than the intermediate diameter with D4, the lead angle of the flat die biting part and finishing part is set to the above setting, so that the worm shaft step in rolling process is almost I was able to make it zero.

  A flat die for worm shaft rolling processing according to a first embodiment of the present invention will be described with reference to FIGS. 1 is a side view of an example of a rolled worm shaft, FIG. 2 is a cross-sectional view of a main part of a flat die for worm shaft rolling according to an embodiment of the present invention, and FIG. 3 is a main part in the direction of arrow A in FIG. FIG. 4 is a side view of the lower flat die 7 for worm shaft rolling processing as an elevational view. FIG. 4 shows the workpiece moved in the axial direction by rolling processing when the flat die shown in FIGS. 2 and 3 is used. FIG. 5 is a graph showing the relationship between the amount of step and the rolling process time. FIG. 5 shows the amount of step that is the amount that the workpiece moves in the axial direction by the rolling process when using the flat die of FIG. FIG. 6 is an elevation view of a conventional lower flat die for worm shaft rolling processing corresponding to FIG. 3.

  As shown in FIG. 2, a worm shaft used for a small motor or the like holds a workpiece 12 that is a cylindrical material rotatably by a center holding device (not shown), and a pair of peripheral surface rolling portions 2 of the workpiece 12. The pair of flat dies 6, 7 are moved in opposite directions while being pressed by being sandwiched between the flat dies 6, 7, thereby rotating the work 12, which is a cylindrical material, and rotating the peripheral surface thereof. 2, the worm gear 4 is formed by plastic working. The center holding device supports both the centers of the workpiece 12 and can follow the step of the workpiece. However, the center holding device may have a bush structure that is fitted to the workpiece handle cylindrical portions 1 and 3 and is rotatable.

In the conventional flat die for worm shaft rolling processing as shown in FIG. 6, since the lead angle of the thread of the tooth surface of the die tooth, that is, the upper surface of the flat die is made constant, the rolling process proceeds. When the rolling diameter of the peripheral surface rolling portion of the workpiece changes accordingly, the workpiece moves in the axial direction as described above, and a step phenomenon occurs. When the inventors perform rolling processing in which the workpiece walking direction is the direction indicated by 13, the worm gear 4 and the workpiece handle portion cylindrical portion on the opposite side to the workpiece walking direction as shown in FIG. We found that the workpiece bends near the boundary of 3.
As shown in FIG. 6, when the workpiece 12 is being processed by rolling, the positional relationship between the flat die 7 at each position and the end of the cylindrical portion of the workpiece handle portion is 15⇒16⇒17, and the radial movement position It changes corresponding to ac. The work 12 walks in the axial direction and the arrow op direction as seen in the figure. That is, assuming that the machining part to be machined by the worm gear 4 is 72, the machining part 72 moves in the direction of the arrow op in the axial direction as the machining of the workpiece handle portion cylindrical part 3 proceeds 15⇒16⇒17. At this time, bending of the workpiece occurred in the vicinity of the worm gear 4 and the handle cylindrical portion 3 opposite to the direction of the arrow op, which is the workpiece walking direction, and the machining accuracy was deteriorated and the effective tooth width of the worm gear was shortened. The graph of FIG. 5 shows the relationship between the amount of step, which is the amount that the workpiece moves in the axial direction by the rolling process, and the rolling process time when the flat die of FIG. 6 is used.

  2 and 3, the worm shaft rolling flat die according to the embodiment of the present invention is disposed between a pair of flat dies 6 and 7 to roll the peripheral surface of a workpiece 12 that is a cylindrical material. In the flat die for worm shaft rolling forming the worm gear 4 in the part 2, the lead angle of the thread at the starting end of the biting part 30 of the flat dies 6 and 7 is β1, the lead of the thread at the end of the finished part 31 of the flat die The angle is set to β2, β1 <β2, and the lead angle is continuously increased from the lead angle β1 at the beginning of the bite portion of the flat die to the lead angle β2 at the end of the finish portion of the flat die. The screw thread is formed by changing it smoothly and smoothly. Thereby, the step in the rolling process can be reduced, and it is not necessary to provide a flat portion with a constant width for the correction die adjacent to the peripheral surface rolling portion 2 of the cylindrical material, and can be applied. The present invention provides a flat die for worm shaft rolling that does not limit the workpiece, that has a small workpiece bending due to rolling, and that does not require a process such as bending correction.

In the worm shaft rolling flat die of the embodiment of the present invention shown in FIGS. 2 and 3, the outer diameter of the workpiece 12 which is a cylindrical material is D0, the outer diameter of the worm gear 4 is D3, and the root diameter of the worm gear is the same. When D4 is set, the lead angle of the thread at the starting end of the flat die biting portion 30 is β1, the designed rolling diameter of the workpiece 12 which is a cylindrical material at the biting portion 30 is D1, and the axial pitch of the worm gear 4 is P. The design rolling diameter of the work 12 which is a cylindrical material at the biting part 30 is D1,
D1 = D0 and ((D0 × 0.95) <D1 <(D0 × 1.05) may be satisfied)
β1 is set so that tanβ1 = P / πD1,
Design the workpiece 12 that is a cylindrical material at the finishing section 31 with β2 as the lead angle of the thread at the end of the flat die finishing section 31 and the design of the workpiece 12 that is the cylindrical material at the finishing section 31 as D2. The rolling diameter is D2, D2 = 1.05 x [(D3 + D4) / 2],
(D2 may be [(D3 + D4) / 2] <D2 <1.1 × [(D3 + D4) / 2]) β2 is set so that tanβ2 = P / πD2.
In addition, the thread angle is formed by continuously and smoothly changing the lead angle from the lead angle β1 of the thread at the start end of the flat die 30 to the lead angle β2 at the end of the finish 31. The rolling diameter of the cylindrical material at the bite portion of the flat die approximates the diameter of the cylindrical material, and the rolling diameter of the cylindrical material at the finish portion is the worm gear outer diameter D3 and the worm gear tooth bottom. Since the diameter is slightly larger than the intermediate diameter with D4, the relative relationship between the flat die 7a and the workpiece 12 is 21⇒22⇒ by setting the lead angle of the flat die biting part and finish part as above. As shown in 23, it is constant without changing as processing proceeds. As a result, the bending of the end portion of the worm gear is small, the machining accuracy is improved, the number of incomplete teeth is small, and the effective tooth width of the worm gear is secured. In the graph of FIG. 4, when the flat dies for worm shaft rolling processing of the embodiment of the present invention shown in FIGS. 2 and 3 are used, the amount of step that is the amount that the workpiece moves in the axial direction by rolling processing, and the rolling As shown in the relationship with the fabrication time, the worm axis step in the rolling process was almost zero.

The side view of an example of the worm shaft which carried out the rolling process. The principal part sectional view of the flat die for worm shaft rolling processing of the embodiment of the present invention. FIG. 3 is a side view of the main part in the direction of arrow A in FIG. 2, in which the lower flat die 7 for worm shaft rolling is viewed as an elevational view. The graph which shows the relationship between the amount of steps which is the quantity which a workpiece | work moves to an axial direction by rolling processing, and rolling processing time when the flat die | dye of FIG. 2, FIG. 3 is used. The graph which shows the relationship between the amount of steps which is the quantity which a workpiece | work moves to an axial direction by rolling processing, and rolling processing time when the flat die of FIG. 6 is used. FIG. 4 is an elevation view of a conventional lower flat die for worm shaft rolling processing corresponding to FIG. 3.

Explanation of symbols

2: Rolled surface of cylindrical material, 4: Worm, 6, 7: Flat die
12: Workpiece made of cylindrical material, 30: Biting portion of flat die, 31: Finishing portion of flat die β, β1, β2: Lead angle of flat die thread

Claims (2)

  In a flat die for worm shaft rolling processing that is disposed between a pair of flat dies and forms a worm gear on a circumferentially rolled portion of a cylindrical material, the lead angle of the thread at the bite portion start end of the flat die is β1, The lead angle of the thread at the end of the flat die is set to β2, β1 <β2, and the screw thread at the end of the flat die from the lead angle β1 of the bite start of the flat die. A flat die for worm shaft rolling processing, wherein the lead angle is continuously and smoothly changed to a lead angle β2 to form a screw thread. In a flat dies for worm shaft rolling processing, which is arranged between a pair of flat dies and forms a worm gear at the peripheral rolling portion of the cylindrical material, the outer diameter of the cylindrical material is D0 and the outer diameter of the worm gear is D3. When the root diameter of the worm gear is D4, the lead angle of the thread at the start of the bite portion of the flat die is β1, the design rolling diameter of the cylindrical material at the bite portion is D1, and the axial pitch of the worm gear is P As
The design rolling diameter of the cylindrical material at the biting part is D1,
(D0 × 0.95) <D1 <(D0 × 1.05) and β1 is set so that tanβ1 = P / πD1.
The lead angle of the screw thread at the end of the finished part of the flat die is β2, the designed rolling diameter of the cylindrical material at the finished part is D2, and the designed rolling diameter of the cylindrical material at the finished part is D2.
[(D3 + D4) / 2] <D2 <1.1 × [(D3 + D4) / 2]
And β2 is set so that tanβ2 = P / πD2.
In addition, the lead angle is continuously and smoothly changed from the lead angle β1 of the screw thread at the leading end of the flat die to the screw lead angle β2 at the end of the finish part of the flat die. A flat die for worm shaft rolling processing, characterized by being formed.

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